Module AmbFunction {
      Function Amb (failure) {
            // get an array of s items, return an array of 1 item
            // we do this so we forget the type of element
            getitem=lambda (n, c) -> {
                  dim z(1) :link c to c()
                  stock c(n) keep 1, z(0)  // copy from c(n) to z(0) one item
                  =z()
            }
            read a
            c1=lambda a, getitem (i, &any,  &ret) ->{
                  any=getitem(i, a)
                  ret=any
                  =true
            }
            m=stack.size
            if m=0 then Error "At least two arrays needed"
            c=c1
            while m>1 {
                  read b
                  c1=lambda c2=c, j=0, m=len(a), b, failure, getitem (i, &any,  &ret) ->{
                        any=getitem(i, b)
                        ret=(,) :  ok=false :  anyother=(,)
                        do
                              if c2(j, &anyother,  &ret) then
                                    if not failure(any, anyother) then
                                          ok=true
                                          ret=cons(ret, any)
                                    end if
                              end if
                              j++
                        until ok or j=m
                        if j=m then j=0
                        =ok
                  }
                  c=c1 :  a=b :  m--
            }
            read b
            amb1=lambda c2=c, j=0, m=len(a), b, failure, getitem (&ret) ->{
                  ret=(,) :  ok=false: anyother=(,)
                  k=each(b)
                  while k
                        any=getitem(k^, b)
                        do
                              if c2(j, &anyother,  &ret) then
                                    if not failure(any, anyother) then
                                          ok=true
                                          ret=cons(ret, any)
                                    end if
                              end if
                              j++
                        until ok or j=m
                        if j=m then j=0
                        if ok then exit
                  end while
                  =ok
            }
            ret=(,)
            if amb1(&ret) then =ret else =(,)  ' default return value
      }

      a=(1, 2, 3)
      b=(7, 6, 4, 5)
      failure=lambda  (a,b)->{
            =a#val(0)*b#val(0)<>8
      }
      Print amb(failure, a, b)#str$()
      a=("the", "that", "a")
      b=("frog", "elephant", "thing")
      c=("walked", "treaded", "grows")
      d=("slowly", "quickly")
      failure=lambda  (a,b)->{
            =left$(a#val$(0),1)<>right$(b#val$(0),1)
      }
      Print amb(failure, a, b, c, d)#str$()
}
AmbFunction